Electroluminescent device



July 4, 1961 B. E. BARTELS 2,991,385

ELECTROLUMINESCENT DEVICE Filed March 20, 1959 INVENTOR BERN/MRO E. BARR-ZS ATTORNEY United States Patent 2,991,385 ELECTROLUMINESCENT DEVICE Bernhard E. Bartels, Glen Cove, N.Y., assignor to Sylvania Electric Products Inc., a corporation of Delaware Filed Mar. 20, 1959, Ser. N0. 800,857 2 Claims. (Cl. 3'1'3-108) My invention relates to electroluminescent lamps.

As is known to the art, an electroluminescent lamp comprises first and second spaced apart electrodes, at least one of which permits the passage of light therethrough. A solid electroluminescent layer is interposed between and in contact with both electrodes. (This layer is either composed entirely of an electroluminescent phosphor or a dispersion of electroluminescent phosphor particles in dielectric material.) When a voltage is applied between the electrodes, light is emitted from the electroluminescent layer.

The electroluminescent layer, particularly when relatively thin, is translucent. By making use of this translucent property, I have succeeded in producing a new type of electroluminescent lamp which, for a given applied voltage, exhibits significantly enhanced brightness. My lamp can be produced rapidly and inexpensively; further, my lamp functions effectively at relatively low voltages.

In accordance with the principles of my invention, a first electroluminescent layer is applied over a first electrode. over the first layer. Thereafter, a second electroluminescent layer is applied over the second electrode. Finally, a third electrode is applied over the second electroluminescent layer. At least one of the first and third electrodes is transparent.

The first and third electrodes are electrically connected in common to a first terminal. The second electrode is connected to a second terminal. A voltage is applied between these terminals, and light is produced.

Since the electroluminescent layers are translucent, most of the light emitted from either layer, which strikes the other layer, passes through this other layer. In other words, each layer contributes to the total light output. Indeed, I have found that the light output from my two layer lamp, for a given applied voltage, is almost twice as large as the light output from a single layer lamp of like geometry.

An illustrative embodiment of my invention will now be described with reference to the accompanying figure.

Referring now to the figure, there is shown a glass plate 10, one side of which is covered with a transparent electrically conductive tin oxide film constituting a first electrode 12. A first electroluminescent layer 14, formed for example of a dispersion of copper activated zinc sulfide electroluminescent phosphor particles in a ceramic dielectric frit, is applied over electrode 12. A second electrode 16 (identical in composition to electrode 12) A second transparent electrode is then applied is applied over layer 14. A second electroluminescent layer 18 (identical in composition with layer 14) is applied over electrode 16. A third electrode 20, in the form of a metal backing plate, is applied over layer 18.

Electrodes 20 and 12 are connected in common to a first terminal 20. Electrode 16 is connected to a second terminal 24. When an alternating voltage is applied between terminals 22 and 24, light from the first electroluminescent layer 14 passes directly through electrode 12 and the glass plate 10. Further light from the second electroluminescent layer 18 passes through electrode 16, the first electroluminescent layer 14 (which is translucent) electrode 12 and the glass plate 10.

This arrangement produces substantially more light than a similar lamp using a single electroluminescent layer. For example, two lamps were constructed, one lamp having a single electroluminescent layer about 1 ml. thick, the other lamp having two electroluminescent layers, each about 1 mil. thick, the lamp geometries being otherwise identical. When a voltage of 110 volts R.M.S. at c.p.s. was applied to each lamp in turn, it was found that the total light output from the two layer lamp was about in excess of the light output from the single layer lamp.

What is claimed is:

1. An electroluminescent device comprising a sandwich like structure including, in the order named, a first electrode; a first solid electroluminescent layer; a second transparent electrode; a second solid electroluminescent layer; and a third electrode, at least one of said first and third electrodes being transparent, said first and third electrodes being connected in common to a first terminal, said second electrode being connected to a second terminal.

2. An electroluminescent device comprising a sandwich like structure including, in the order named, a first electrode; a first solid electroluminescent layer; a second transparent electrode; a second solid electroluminescent layer; and a third electrode, at least one of said first and third electrodes being transparent; said first and third electrodes being connected in common to a first terminal, said second electrode being connected to a second terminal, and means to apply a voltage between said first and second terminals to energize said layers whereby light is emitted therefrom.

References Cited in the file of this patent UNITED STATES PATENTS 2,768,310 Kazan Oct. 23, 1956 2,866,117 Walker Dec. 23, 1958 2,867,739 Michlin Jan. 6, 1959 2,931,915 Jay Apr. 5, 1960 FOREIGN PATENTS 787,401 Great Britain Dec. 11,- 1957 

